This invention relates generally to cable connectors for electric power systems, and more particularly to separable insulated loadbreak connector systems for use with cable distribution systems.
Electrical power is typically transmitted from substations through cables which interconnect other cables and electrical apparatus in a power distribution network. The cables are typically terminated on bushings that may pass through walls of metal encased equipment such as capacitors, transformers or switchgear.
Separable loadbreak connectors allow connection or disconnection of the cables to the electrical apparatus for service, repair, or expansion of an electrical distribution system. Such connectors typically include a contact tube surrounded by elastomeric insulation and a semiconductive ground shield. A contact piston is located in the contact tube, and a female contact having contact fingers is coupled to the piston. An arc interrupter, gas trap and arc-shield are also mounted to the contact tube. The female contact fingers are matably engaged with an energized male contact of a mating bushing, typically an elbow connector, to connect or disconnect the power cables from the apparatus. The piston is movable within the contact tube to hasten the closure of the male and female contacts and thus extinguish any arc created as they are engaged.
Such connectors are operable in “loadmake”, “loadbreak”, and “fault closure” conditions. Fault closure involves the joinder of male and female contact elements, one energized and the other engaged with a load having a fault, such as a short circuit condition. In fault closure conditions, a substantial arcing occurs between the male and female contact elements as they approach one another and until they are joined in mechanical and electrical engagement. Such arcing causes air in the connector to expand rapidly accelerating the piston. A rigid piston stop is typically provided in the contact tube to limit movement of the piston as it is driven forward during fault closure conditions toward the mating contact.
It has been observed, however, that sufficient energy can be generated that rapidly expands the air present in the connector during a fault-close operation that slowing or stopping the piston using a typical piston stop can not be achieved in the length of travel available. If the piston can be prevented from accelerating to a high speed or slowed prior to engaging the piston stop, the piston may exit the bushing leading to uncontrolled arcing and fault to ground.